Thermosetting organosiloxane composition

Abstract

The combination of a microencapsulated hydrosilylation catalyst selected from the group consisting of metals from the platinum group of the periodic table and compounds of these metals and a known inhibitor for this type of catalyst impart excellent storage stability to organosiloxane compositions that cure by a hydrosilation reaction while enabling these compositions to rapidly cure at temperatures above the softening temperature of the thermoplastic resin used to encapsulate the hydrosilylation catalyst. The curing rate of the composition is faster relative to compositions containing the microencapsulated catalyst without the catalyst inhibitor.

That which is claimed is: 
     
       1. In a thermosetting organosiloxane composition comprising (A) an organopolysiloxane having at least two silicon-bonded alkenyl groups in each molecule and represented by the average unit formula   R.sub.a SiO.sub.(4-a)/2        wherein R is a substituted or unsubstituted monovalent hydrocarbon radical an the value of a is from 1.0 to 2.3;   (B) an organohydrogenpolysiloxane containing at least two silicon-bonded hydrogen atoms in each molecule in an amount sufficient to cure said organopolysiloxane;   (C) an amount of a hydrosilylation-reaction catalyst sufficient to promote curing of said composition, where said catalyst is microencapsulated by a thermoplastic resin exhibiting a softening point of 40 to 250 degrees Centigrade; the improvement comprising the presence in said composition of     (D) a hydrosilylation reaction-inhibiting compound selected from the group consisting of (1) compounds containing at least 1 alkynyl group in each molecule, (2) organosilicon compounds selected from the group consisting of ##STR3##  and (3) disiloxanes and cyclotetrasiloxanes containing at least one bonding unit in which an alkenyl radical is bonded to each of two silicon atoms joined through an oxygen atom bridge, where the amount of said inhibiting compound is sufficient to accelerate curing of said composition at temperatures above the softening point of said thermoplastic resin.   
     
     
       2. A thermosetting organopolysiloxane composition according to claim 1 in which the thermoplastic resin is selected from the group consisting of polystyrene, polymethyl methacrylate, silicone resins and polysilanes, the hydrosilylation-reaction catalyst is a metal from the platinum group of the periodic table or a compound of said metal and is present at a concentration of from 0.000001 to 0.1 part by weight, based on platinum, per 100 parts by weight of said organopolysiloxane, the boiling point of said inhibiting compound is at least 80° C., the concentration of said inhibiting compound is from 0.00001 to 5 parts by weight per 100 parts of said organopolysiloxane, and R represents at least one member selected from the group consisting of alkyl, alkenyl, aryl, and halogen-containing alkyl radicals, 
     
     
       3. Thermosetting organopolysiloxane composition of claim 2 wherein the hydrosilylation catalyst is a platinum/alkenylsiloxane complex, R is at least one member selected from the group consisting of methyl, phenyl and 3,3,3,-trifluoropropyl, said organopolysiloxane is a polydiorganosiloxane, and the concentration of said hydrosilylation reaction catalyst is equivalent to from 0.00005 to 0.01 part by weight of platinum per 100 parts by weight of said organopolysiloxane. 
     
     
       4. A thermosetting composition according to claim 1 where said disiloxanes and cyclotetrasiloxanes containing at least one bonding unit in which an alkenyl radical is bonded to each of two silicone atoms joined through an oxygen atom bridge are selected from the group consisting of 1,3-divinyltetramethyldisiloxane, 1,3,5,7-tetravinyltetramethylcyclotetrasiloxane, and 1,3-divinyl-1,3-diphenyldimethyldisiloxane.